Many wireless networks, such as cellular phone networks, involve a combination of network infrastructure and mobile devices. In the case of a WiFi network, the network infrastructure is referred to as an “access point,” in cellular networks it is typically referred to as a “Base Station,” or “eNB”. For purposes described here, these are all equivalent. Similarly, for WiFi networks, the mobile devices are typically called “client” devices and for cellular networks they are usually called “handsets,” or “subscriber devices.” For purposes described here, they are interchangeable.
Frequently, the network infrastructure is mounted at an elevated location, such as on a tower, while the users are typically at ground level. In such a situation, the radio wave propagation is affected in unpredictable ways by objects in the environment, such as trees, buildings and so forth. Radio signals will often follow the roadways in urban canyons, bouncing back and forth between buildings, and not following a direct line between the emitter and receiver. This unpredictable behavior makes it quite difficult to plan a wireless network.
Locations for towers and base stations can be hard to obtain, and once obtained, it can be difficult to predict precisely what kind of antenna will best provide coverage to the required area near the base station site. Because towers can be so difficult to obtain, those that are available are often not ideally located to provide wireless coverage.
Historically, the network operator has had a selection of standard antennas for their base stations. For example, they might choose to use an omnidirectional antenna, a 90 degree sector, or a 120 degree sector. Each of these antennas is manufactured with dimensions to achieve the desired radiation pattern. The radiation pattern of an antenna is always described in an anechoic environment—one where there are no reflections or objects to absorb signal energy.
However, because of the characteristics of the propagation environment described earlier, it has historically required a great deal of trial and error (or possibly experience) to predict how a particular antenna would perform in a given real-world situation.
Typically, the way a network operator would deal with this situation was through trial and error. They would make an educated guess as to the best antenna to use in a particular situation, they might do some simulation to estimate coverage, and then perform a “site survey,” driving around in a dedicated vehicle with specialized test equipment and collecting data on the wireless coverage. Based on the results of the drive test, they might change antennas at the base station or adjust the aiming of the antennas to address problem spots, and then repeat the drive test, to make sure that fixing one problem didn't introduce a new problem.
This works well enough, but it is labor intensive and only provides a “snapshot” in time of network performance. The process only characterizes the network performance at the time when the site survey was conducted. If a building is constructed, or foliage conditions change, the wireless propagation characteristics will also change, frequently in unpredictable ways. Also, if an antenna needs to be adjusted, it involves visiting the site and possibly climbing a tower and then conducting another site survey—a labor intensive and expensive exercise.